This invention relates to instruments for performing surgical procedures. More particularly, it relates to the clamping mechanism of these instruments which enables the surgeon to clamp or grasp bodily tissue especially during endoscopic surgical procedures.
During an endoscopic surgical procedure, access to the surgical site within the body cavity is provided through openings of a small diameter made in the body wall. An instrument frequently used to provide this access is the trocar. The trocar is an assembly which includes an obturator and a cannula. The obturator has a sharp tip which is used to puncture the body wall to provide the access opening. The obturator slides within the cannula, which is a hollow, cylindrical sleeve. When the obturator has punctured the body wall, the obturator is removed from the cannula. The cannula, however, remains in place within the opening made in the body wall by the obturator. Consequently, the cannula provides a cylindrical passageway to gain access to the surgical site within the body cavity.
Accordingly, a characteristic feature of many endoscopic surgical instruments is a long cylindrical shaft which can slide through the trocar cannula. At the business end of the shaft, which is the end of the instrument coming into contact with tissue at the surgical site within the body cavity, an "end effector" is provided to manipulate the tissue in some way to carry out a desired surgical procedure. The business end, including the end effector, must likewise be capable of sliding through the trocar cannula. At the opposite end of the shaft, there is an actuator operatively connected to the business end to remotely control the performance of the end effector. The actuator is conveniently housed in a frame which may include a pistol grip handle with one or more pivoting triggers. Alternatively, the actuator may include a lever, or the combination of a pivoting trigger and a lever. The actuator is activated when the surgeon pivots the trigger or depresses the lever. These actions in turn cause the end effector to perform its desired function.
One particularly desired function of an end effector of an endoscopic surgical instrument is the ability of the end effector to clamp or grasp tissue. It may be necessary to gasp tissue so that it may be retracted or otherwise precisely positioned to carry out a particular procedure. Instruments which carry out these functions are conveniently referred to as graspers and retractors. In some procedures, it is desirable to clamp tissue so that the clamped tissue may be fastened when staples are fired into and through the tissue. Instruments with end effectors which fire staples into clamped tissue are referred to as linear staplers and cutters (cutters are so named because they simultaneously cut the tissue with a knife between rows of fired staples).
The end effector of an endoscopic surgical instrument which can clamp or grasp tissue typically has two opposed, elongated jaws. The jaws have internal tissue-contacting surfaces between which the tissue is clamped or gasped. The jaws are often described as a lower jaw and an upper jaw. The lower and upper jaws move relative to each other. When the jaws are moved to an open position, the tissue clamping surfaces of the jaws are spaced from each other so that tissue can be placed between the two surfaces. When the jaws are moved to their closed position, the tissue-contacting surfaces of the jaws are positioned adjacent each other so that tissue placed between the jaws is clamped or grasped. Often, the tissue-contacting surfaces of graspers may be serrated to provide an enhanced surface for grasping tissue, and both jaws pivot between their opened and closed positions. Linear cutters and staplers have conventionally had a fixed lower jaw and a pivoting upper jaw which pivots from open to closed positions relative to the lower jaw. The fixed lower jaw may include a channel for receiving a staple cartridge. The upper jaw typically includes an anvil. Accordingly, when a linear stapler or cutter is used, tissue is placed between the cartridge and anvil when the upper jaw is in the open position, the upper jaw is pivoted to its closed position to clamp tissue between the cartridge and anvil, and staples are subsequently fired from the cartridge into the clamped tissue for formation against the anvil.
A key feature of the clamping and grasping mechanisms of endoscopic surgical instruments is the mechanism which causes the upper or lower jaw to move from an open position for placing tissue between the jaws to a closed position for clamping that tissue. A common mechanism, particularly for endoscopic linear cutters, involves the use of a "camming" closure tube. This tube reciprocates back and forth. In its rearward position, the jaws are in the open position. In its forward most position, the upper jaw has pivoted to its closed position so that the anvil and cartridge are adjacent each other. In its rearward position, the distal end of the tube is positioned proximally of the upper jaw (in other words, the tube sits behind the jaw). The upper jaw, which is more frequently referred to simply as the anvil, has what is referred to as an outer, ramped camming surface at its proximal end. When the tube reciprocates from its rearward to forward position, the distal end of the tube slides along, or "cams" against the outer camming surface of the anvil. This camming action causes the anvil to pivot from its open to closed position.
Unfortunately, the camming mechanism for causing opposed jaws to clamp or grasp tissue placed between them is undesirably inefficient. There are high frictional losses associated with the camming action as the distal end of the tube slides against the ramped camming surface of the anvil. These high frictional losses create poor efficiency for the mechanism. When the mechanism is inefficient, higher forces are necessary to actuate the clamping mechanism. In other words, the surgeon using the instrument will need to exert more pressure when he squeezes the trigger or depresses the lever to actuate the clamping mechanism so that the jaws close. Obviously, precise positioning of the end effector is hampered and frustration mounts as the amount of pressure which the surgeon must apply to damp increases.
Another difficulty with the use of the closure tube for camming is the requirement for the ramped camming surface on the anvil. This surface is really "wasted" surface area on the anvil because that portion of the anvil where this surface is positioned may not be used to form staples. The staple-forming surface of the anvil, which is the internal tissue-contacting surface, has pockets or depressions embedded in it where staples fired from the cartridge are formed. The inner surface of the portion of the anvil which is opposite the outer, ramped camming surface cannot, by its nature contain the pockets or depressions for staple formation. Therefore, staples are not formed along the entire length of the inner surface of the anvil. This means that the anvil is longer than it needs to be. Consequently, when tissue is clamped between the jaws, the jaws may undesirably "flex" or twist. This can frequently be a problem when thicker tissue is clamped between the jaws, because the force necessary to clamp thicker tissue is greater than the force necessary to clamp thinner tissue. When flexing or twisting of the jaws occurs, it may cause the staples to malformed when they are fired, resulting in improperly fastened tissue.
Another problem with the ramped camming surface is that because it necessitates the use of an anvil which is longer than the tissue-contacting surface of the cartridge, it becomes necessary to incorporate a "tissue stop" onto the anvil. The tissue stop retards the passage of the tissue placed between the jaws into that portion of the anvil opposite the ramped camming surface where staples cannot be fired. The tissue stop is typically a pair of lateral surfaces descending from the elongated anvil body. These lateral surfaces come into contact with the tissue when the tissue is placed between the jaws, and therefore impede further proximal movement of the tissue. Unfortunately, the tissue stop is sometimes ineffective to prevent rearward passage of tissue, and this, of course, can result in improperly fastened tissue.
Another difficulty observed in connection with the cam closure mechanism is that the opening between the jaws when the jaws are in the open position, or "gap", created when the anvil has a ramped camming surface is less than what is desired. The greater the gap, the better. This is because a wider gap enables the surgeon to more easily position the tissue between the jaws before clamping. Proper tissue positioning increases the likelihood of proper staple formation. In addition, after staples are fired, the jaws are returned to the open position, and often it is necessary to remove the spent staple cartridge and reload it with a new one for a subsequent firing. Once again, a greater gap makes it easier for the surgeon or operating room assistant to remove a spent cartridge and reload it with a new one.
Finally, the cam closure mechanism suffers from a further deficiency. If a downward force is applied to the distal end of the anvil when the end effector is positioned at the surgical site within the body cavity, the anvil will pivot from its open to closed position. This frequently occurs when the anvil brushes up against bodily tissue or organs. This inadvertent closure can cause disruption and loss of time during a surgical procedure. Furthermore, because the anvil does not have a "positive" opening position, or securely fixed open position, the end effector is incapable of acting as a forceps or graspers. This limits the flexibility and desirability of the instrument as a whole.
Another clamping mechanism is described in Russian Patent No. 728,848. This mechanism also has a reciprocating closure tube which moves from rearward to forward positions for pivoting an anvil from an open to closed position. Lateral pins are attached to the anvil, and the closure tube rides on these pins within slots on the closure tube. While this mechanism avoids some of the deficiencies associated with a closure mechanism which has a ramped camming surface on the anvil, it still requires relative movement between the closure tube and the anvil. Consequently, not all of the anvil may be used for staple formation. The greater anvil length may create flexing or twisting when thick tissue is clamped, potentially resulting in staple malformation. The gap between the tissue-contacting surfaces when the anvil is in the open position is still less than desirable.
Therefore, in view of the deficiencies inherent in those clamping mechanisms for endoscopic surgical instruments which have been previously described, an endoscopic surgical instrument with a better clamping or grasping mechanism is desired. This clamping mechanism would cause relative movement of the jaws of the end effector of the instrument from an open position where tissue can be placed between the jaws to a closed position for clamping or grasping of that tissue. The mechanism would reduce frictional losses and therefore provide greater efficiency than those mechanisms which have been described in the literature or elsewhere. It would also take full advantage of the entire length of the upper jaw, which frequently represents the anvil, and consequently reduce flexing or twisting of the jaws when tissue is clamped. Additionally, an efficient clamping mechanism which enables the creation of a wider gap between the jaws in the open position would facilitate the positioning of tissue in the jaws as well as cartridge removal and reloading. Furthermore, it would be desirable if such a clamping mechanism could be developed which provides for a positive opening between the jaws in their open position so that the jaws can be used as forceps or graspers.